Ip helper-address

in TSHOOT topology, we have a DHCP client (client1) on vlan 10. Broadcast traffic from the client to the DHCP server should be allowed to pass through DSW1 and DSW2. So where to put “ip helper-address”? it depends on which switch will take the HSRP Active state.
First, check the spanning-tree instance on vlan 10. Then, see which is the HSRP Active gateway. If for example DSW1 is the Active HSRP, then “ip helper-address AddrA” should be put under “interface vlan 10” of DSW1.
Beware that AddrA is the ip address of R4 interface. And this value is:
–, if DSW1 is HSRP Active gateway,
–, if DSW2 is HSRP Active gateway.
This took me an hour or so to figure out, maybe because I’m a little tired :-)


  1. May 26, 2011

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